BANGKOK -- A Myanmar military offensive against ethnic rebels in the country's east has uprooted more than 10,000 people, rights groups said, accusing the army of bombing schools and Buddhist temples, firing on civilians and raping women.

Since Oct. 6, the army has shelled six villages, shot and injured three people, and fired on 17 villagers who are now missing, according to activists in Shan state.

The Shan Human Rights Foundation has documented eight cases of sexual violence since April 2015, including a 32-year-old woman gang-raped by 10 soldiers on Nov. 5 while her husband was tied up under their farm hut in Ke See township.

"We are very concerned that there has been no public condemnation by the international community about these war crimes and these attacks on civilians," rights activist Charm Tong told the Thomson Reuters Foundation.

Myanmar, formerly known as Burma, has fought ethnic groups in its borderlands off and on for decades, causing massive displacement within the country and forcing hundreds of thousands to seek refuge across the border in Thailand.

In 2010, the country's ruling military junta was replaced by a military-backed civilian government, and the country embarked on reforms towards elections earlier this month, which saw opposition leader Aung San Suu Kyi's National League for Democracy win in a landslide.

"We welcome a beautiful election on one side, but the other reality is that people are fleeing, dying, women are being raped," Charm Tong said.

"Villagers are still not safe and are in a dangerous situation now because of the Burma army presence is increasing."

The Myanmar government did not respond to requests for comment about the fighting in Shan state.

The government in October signed a ceasefire with eight armed ethnic groups, but the deal fell short of its nationwide billing, with seven of the 15 groups invited declining to sign, including the Shan State Army-North (SSA-North) and the Kachin Independence Army (KIA).

Shan state, which borders Thailand, Laos and China, is rich in resources and the site of three hydroelectric dam projects.

The latest attacks come as villagers in the area prepare for the rice harvest. Many are stealthily returning home to collect their belongings and tend to their rice paddies, but the situation remains unstable, the Shan groups say.

U.S. Assistant Secretary of State Daniel Russel, after talks this week with Myanmar armed forces chief Min Aung Hlaing, described the military operations and fighting in Shan and neighbouring Kachin state as "very worrisome".

"We have concerns about the humanitarian crisis that is generated by the fighting. We also have concerns that the fighting could set back the effort to build out a nationwide ceasefire to include non signatories," Russel told Reuters in Yangon.

"While there are two sides to the conflict, I urged the Burmese military to exercise restraint and to work in an effort to promote reconciliation and peace."

The United Nations is also concerned about the fighting and reported up to 6,000 displaced people seeking refuge in monasteries and temporary shelters, said Pierre Peron, spokesman for the U.N. Office for the Coordination of Humanitarian Affairs (OCHA).

Peron said the U.N. and aid groups are working with local organisations in Shan state to provide immediate humanitarian needs, including hygiene kits, clothing, blankets, food, medicine, shelter and water purification tablets.

"A U.N.-led team managed to visit some of the displaced people last week. We will continue to monitor the situation closely and are ready to provide further support as soon as security conditions allow," Peron said.

In an update on Friday, OCHA said fighting between the government and ethnic rebels in Kachin state had displaced 1,200 people, including 500 children.